Electronic flash lighting system



Sept. 20, 1960 J. E. CHAUVINEAU 2,953,721

ELECTRONIC FLASH LIGHTING SYSTEM Filed 001:. 25, 1957 2 Sheets-Sheet 1TEEN- I Tluzra f 1 BY w 444 ATTORNEY Sept. 20, 1960 J. E. CHAUVINEAU2,953,721

ELECTRONIC FLASH LIGHTING SYSTEM Filed Oct. 25. 1957 2 SheetMheet 2'Tzqj.

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ATTORNEY United States l atent ELECTRONIC FLASH LIGHTING SYSTEM JeanEmilien Chauvineau, Rue Charles Lecocq (Seine et Oise), Lozere, France,assignor to F. Alexander, New York, N.Y.

Filed Oct. 25, 1957, Ser. No. 692,351

6 Claims. (Cl. 315-241) The present invention relates to electronicflash lighting systems and a method of operating the same, moreparticularly, to flash lighting systems for use in high speed flashphotography, motion picture photography, light signaling, stroboscopes,marine or land beacons and other uses and'applications, where a highintensityand easily controllable light source is required.

Conventional high intensity electronic flash lights es- :sentiallycomprise a gaseous discharge tube consisting of a glass envelope filledwith a suitable rarefied gas or :mixture of gases, such as argon, neon,crypton, xenon, \etc. at a suitable pressure, and a pair of maindischarge electrodes providing an ionic or gaseous discharge path'within said tube. One of said electrodes constituting the cathode orelectron emissive element consists of or is :coated with a suitableelectronically active material to emit electrons under the eifect of thenegative voltage gradient, upon application of a suitable direct currentoperating voltage to the tube, While the other electrode constitutes theanode or electron collecting element well Iknown to and understood bythose skilled in the art.

Gas discharge devices including flash tubes normally present a highimpedance to the passage of an electric :current and, in fact, suchtubes may be regarded as a 'current interrupter or insulator underordinary condi- ';tions. If, however, a potential difierence or voltageof a :suificiently high value, that is, exceeding the ionization torbreakdown potential of the tube, is applied to the cube, the impedanceof the tube changes suddenly to a very low value. This, in turn, maycause a considerable current flow in the form of a high intensity lowvoltage are through the tube accompanied by a light flash having anintensity and spectral composition depending upon the nature, pressureand other characteristics of the gas and design features of the tube.

This sudden change of the tube from an insulator to :an extremely lowimpedance is the result of the cumulative ionization of the gasmolecules by the free electrons being accelerated in the direction fromthe cathode towards the anode and producing an ever increasing number ofnew ionizing electrons upon collision with the gas molecules, providedthe applied voltage has a certain minimum, known as the critical orionization voltage of the tube.

Instead of varying the main operating or discharge voltage, the lattermay have a fixed value below the ionizing or breakdown point of thetube, while the ionization and ignition of the tube is eifected by meansof an ionization or triggering potential applied to a suitable auxiliaryor starting electrode. The latter may be applied either to the outsideof the tube wall, in the form of a coiled wire, metal coating or thelike, or interposed in the discharge path in the form of a starting gridor the like, in a manner well known in the Ordinarily, a tube of theabove type would be destroyed by the intense breakdown (short-circuit)current, unless it were protected by a series or limiting imped ance, ifthe operating voltage is applied over an extendice which is the factthat the instantaneous current or light 7 flash can be producedefliciently and reliably if the duration or flash period is relativelyshort, say about one millisecond or less, as used for high speed flashphotography and similar applications. On the other hand, if

a relatively stronger light source is required or if the flash durationis to be increased appreciably, such as, for instance, for use in lightsignaling, beacon lights, etc., the storage capacitors and accessoryequipment, such as the rectifier power supply etc., will assume suchdimensions and bulk as to render the use of this type of dis chargedevice uneconomical, if not prohibitive, for a great many uses andpractical applications.

The reason for these limitations and shortcomings of the conventionalcapacitor type electronic flash lights is the fact that the totalelectric energy converted into light energy in the flash discharge mustbe stored by the capacitor, that is, the capacitor must have a dimensionand operating voltage suflicient to handle the total output energy ofthe flash, whereby to greatly limit the po tentialities and flexibilityof the conventional capacitor duration of the flash. 7

Accordingly, an important object of the present invention is theprovision of an improved flash lighting system for producing light'ofhigh intensity and/ or duraton, utilizing a flash discharge tube as alight source, which substantially overcomes the above and relateddrawbacks and difficulties inherent in the conventional capacitor typeelectronic flash devices heretofore known intheart.

Another object of the invention is the provision of a flash lightingsystem comprising a capacitor controlled ionic flash tube combined withmeans for direct energization of the tube from a suitable power source,to both increase or control the total light output and/or to extend thelength or duration of the flash produced.

A more specific object of the invention is the provision of a capacitortype ionic flash lighting system including means to increase both thepower and/ or duration of the light flash beyond the limit determined bythe size of or energy of the storage capacitor.

Another object of the invention is the PI'OVlSlOll of a readilycontrollable high intensity light source utilizing pacitor type flashlighting system, known in the art of;

flash photography, stroboscopes and the like;

Fig. 2 is a graph explanatory of the function and operation of theinvention; 7

Fig. 3 is a circuit diagram of an A.C.-operated flash lighting systemembodying the principles of the invention;

Figs. 4 and 5 are further graphs explanatory of the function of Fig. 3;v

Fig. 6 is a circuit diagram showing a modification of a flash lightingsystem according to the invention, designed for producing a practicallyuniform high intensity light output during prolonged and readilycontrollable time periods;

Figs. 7 and 8 are graphs explanatory of thefunction and operation ofFig. 6;

Fig. 9 is a circuit diagram showing yet another modification of anA.C.-operated flash lighting system accord-- ing to Fig. 3;

Fig. 10 is a basic diagram of a D.C.-operated flash lighting systemembodying the principles of the invention;

Fig. 11 is a more detailed circuit diagram of a system operating voltagesource, such as a battery, D.C. gen-f erator or alternating currentgenerator or network connected to a storage capacitor of relatively lowcapacitance, compared with the storage capacitor of a conventionalcapacitor type flash lighting system, said capacitor being,

in turn, shunted by a rarefied gas flash discharge tube of the typedescribed above.

In place of the usual current limitingimpedance, there is connected inseries with the operating source and flash discharge tube, according toone embodiment of the invention, an auxiliary gas discharge or switchingtube acting as a periodic interrupter and being controlled by a sourceof highly peaked ionizing voltage pulses, which latter may be furtherapplied to or serve to periodically ionize the flash discharge tube. Asa result, the impedance of said switching tube varies alternatelybetween relatively low and high values at the rhythm of and insynchronism with the ionizing voltage pulses, in such a manner as tocause the latter to be applied intermittently to said flash tube duringthe low impedance periods of said switching tube, on the one hand, andtoprovide high impedance periods, to result in ready extinction of thetube during the spacing intervals between the ionizing pulses.

The capacitor acting as a stabilizing means is charged intermittently bythe operating source until assuming a charging voltage to enable theionizing voltage pulses to initiate the breakdown of the flash dischargetube. Since the latter is connected during the discharge periods to theoperating source without a high series impedance, due to the action ofthe switching tube, the major portion of the power for the light flashwill be directly supplied from said source, while an excessive dischargecurrent is prevented as a result of the intermittent operation orperiodic extinction of the discharge, in a manner further understoodfrom the following.

The storage capacitor in a system according to the invention suppliesonly a relatively small fraction of the total power or energy convertedinto light by the gas discharge, and among other functions, serves tocontrol the initiation of the discharge flashes and to stabilize theoperation of the system, in such a manner as to enable a reliable andeflective control of both the intensity and duration of the flashdischarge. As a result, the system becomes suited for an increasingnumber of practical applications, such as for optical signaling,

light beacons and the like.

Referring more particularly to Fig. 1, there is shown a basic diagram ofa conventional capacitor type flash discharge system as used inhigh'speed flash photography and for similar applications, comprising adirect current' '4 fier power supply, connected to a storage capacitor11 through a series of limiting impedance, such as a high ohmic resistor12. As a result, the capacitor 11 will be charged gradually according toan exponential charging curve to the full operating voltage of thesource 10 which has a value below the ionizing or breakdown potential ofthe flash tube 13 connected across said capacitor, the total charge E ofthe capacitor being determined by the equation E=V2 CV wherein 0represents the electric capacitance and V represents the voltage of thesource 10.

In order to start or initiate the flash discharge there is furtherprovided a starting or trigger circuit connected across the capacitor 11and comprising a resistance 17 and relatively small capacitor 18 inseries. As a result, a charge will be stored in the capacitor 18, whichupon momentarily closing of the switch 20 discharges suddenly throughthe primary of a trigger transformer 21, whereby to cause a high voltagesurge to be induced in the transformer secondary and to be applied tothe starting electrode 16 of the tube 13 having a cathode 14 and anode15.. As a' result, the gas within the tube becomes ionized to an extentto reduce theirnpedance of the tube to an extremely low value and tocause the storage capacitor 11 tobe discharged through the tube in theform of a short and high peaked luminous flash. At the same time, thelimiting resistance 12 prevents a direct short-circuit current from thesource or battery '10 through the tube 13, thus preventing destructionof the tube and other parts of the circuit. Only after the capacitor 11has again been charged by the source 10 will the system be ready forproducing a new discharge flash upon closing the switch 20, in a mannerwell known to and understood by those skilled in the art.

While capacitor discharge systems of this type have been found to havemany uses where a relatively short flash of limited power is required,such as in high speed photography, stroboscopic applications, etc., thedevice becomes more and more bulky and inconvenient to handle, as wellas expensive, in light signaling, flashing light beacons and similarapplications. The main reason for the disadvantages and shortcomings ofthe conventional capacitor type flash system, according to Fig. 1, liesin their, basic operation and requirement that the total electrical.energy converted into light must be stored in the capacitor 11, thusnecessitating the use of bulky capacitor units and/or high operatingvoltages as the demand for greater power or light output and flashduration increases.

Referring to Fig. 3, there is shown a circuit diagram of anA.C.-operated flash lighting system according to the invention producinglight flashes of increased intensity and/or duration and utilizing inpart the energy stored in a capacitor and in part energy directlysupplied from an operating or power source 22. The latter, which may bea 60 cycle power line or network, feeds a pair of transformers 25 and 26which serve to supply operating voltage to both the ionizing pulsegenerator 27 and the flash tube 13, respectively, the latter beingshunted by stabilizing a capacitor 30. Connected between the transformer22 and a capacitor 30 is an electronic switch in the form of a gasdischarge tube 28 having a pair of main electrodes and an auxiliary orstarting electrode 29.

The ionizing pulse voltage generator may be of any suitable type, and,in the example shown, comprises a screen grid vacuum tube 27 having itsanode energized by the source 22 through the supply transformer 25. Thegrid of tube 27 is excited or controlled, by way of a grid couplingcapacitor 31 and grid leak resistance 32, by a square wavevoltage orseries of rectangular voltage pulses p obtained, for instance, from aconventional square voltage generator (not shown), such as amultivibrator, blocking oscillator, etc. As a result, current pulseswill be set up in the output of the tube during the positivealternations of the anode voltage in rapid sequence, resulting in astorage of magnetic energy in peaking inductance 34 inserted in theanode circuit and the generation of induc- 3 tive'volt'afge peaks 1 Fig.2,, at the instants of cessation of each anode 'current pulse orcollapse of the magnetic field of the coil 34. The ionizing voltagepulses which, by proper design of the peaking coil 34 to have a naturalfrequency equal to the pulse repetition frequency, have a peak amplitudemany times the amplitude of the plate voltage and serve to control theionization of both the flash tube 13 and the switch tube 28.

In the example shown, the ionizing voltage pulses 1?, instead of beingdirectly app-lied to'the flash tube 13, are impressed upon the separatestarting electrode 16 by way of a current interrupter, such as arotating cam 33 having contacts 37 and being driven by a synchronousmotor (not shown) energized by the source or network 22. Similarly, theswitch tube 28 has a starting or ionizing electrode 29 excited by thepulses p through a preferably adfjustable coupling capacitor 35. Boththe flash tube 13 as well as the switch tube 28 may, however, bedirectly excited by the ionizing pulses, as shown in subsequent figures.Fig. 2 shows the usual operating characteristic of a gaseous dischargetube representing current i as a function of applied voltage e. Thecritical or breakdown voltage is shown at e coinciding with the bent orpoint P of the (curve, while e represents the source voltage and e" thevoltage of the pulses p.

The operation of the system according to Fig. 3 will :now be describedwith further reference to Figs. 4 and 5.

Assuming the cam 33 to be designed and/or operated so as to apply aseries or train of ionizing pulses p to the :starting electrode 16 ofthe flash tube 13 during a single :altern-ation or half-cycle a of thepower supply, such as, :for example, during the first, third, fifth,etc. alternation, :as shown in Fig. 4, the capacitor 30 will be chargedduring the intervening alternations through the tube 28 having itsimpedance reduced to zero by the ionizing pulses p wvhich aresimultaneously applied to the control electrode .29 in synchronism withthe control of the flash tube 13. .T he design of the circuit and theamplitude of the operating voltage are such that the capacitor 30 willbe charged to a voltage sufficiently below the ionizing voltage of the'fiash tube 13 to prevent a direct discharge in the absence (of anionizing or triggering pulse p.

On the other hand, during the closing of the contacts .37 of the cam 33,the flash tube 13 becomes ionized by the pulses p simultaneously withthe tube 28, whereby to cause the capacitor 30 to be discharged and toproduce a :series of high intensity luminous flashes through the tube313. Since the tube 28, being in series with the tube 13 :and powersource, offers a relatively low impedance dur- .ing the periods A! ofthe ionizing pulses p, Fig. 2, a sup- ;plementary relatively heavycurrent is caused to flow directly from the source 22 and transformer 26through the flash tube 13, resulting in an increase of both the lightoutput as well as an increase of the flash duration, as

:shown in Fig. 4. In the latter, f represents the peak or dischargecomponent resulting from the capacitor charge CV 2 and 1 indicates theenergy component directly supplied by the power source and being equalto V /Z, where Z is the impedance of the circuit.

There is thus provided by the invention a luminous flash dischargesystem enabling the production of single flashes of increased intensityand duration simply and efficiently by means of a relatively smalldischarge capacitor, being practically of the order of about 100 to 150mfd. and serving mainly as a means to control and stabilize theoperation of the system.

As is well known, the relatively short life of the conventionalcapacitor type flash tubes is due primarily to the moleculardisintegration of the electrode material by the intense instantaneousdischarge peaks caused by the sudden release of the energy stored in therelatively large capacitors required by the conventional systems. Thisdefect is greatly minimized or eliminated by the invention whichutilizes only a relatively small-storage capacitor as a stabilizingmeans with the main discharge energy being supplied directly by thepower source.

Instead of the flash discharges being separated by a single alternationa of the operating voltage, as shown in the drawing, Fig. 5, thecapacitor 30, by suitable design of the cam 33, may be charged by agreater number of intervening alternations, to suit existing conditionsand requirements.

The system according to Fig. 3 may also be operated to produce adischarge of the tube 13 during each positive alternation a: of theoperating source, to provide effective continuous light output composedof a series of discrete short periods'or light flashes, that is, 60flashes in case of. a standard 60-cycle network or operating source. Inthis case, the cam 33 may be dispensed with or designed to close thecontacts 37 during each positive alternation m of the supply current, toproduce a series of discharges of the tube 13 during a desired timeperiod, by closing a control switch 36 of the ionizing pulse generator.

The direct discharge component has the further effect of preventing thecapacitor from discharging completely, in such a manner that during thenext following positive alternation a, the capacitor will again becharged during a fraction, say one-third of the next alternation, to avalue sufiicient to result in additional flash discharges during thesubsequent alternations having a reduced initial discharge peak 7", Fig.5, and providing a practically continuous light output suitable for manypractical uses, such as light signaling, beacon lights, etc. Accordingto a practical example, the full charging voltage V may be about 1500 to2000 volts and the reduced charging voltage V may be about 500 volts,while the ionizing peaks p may be from 4000 to 5000 volts at arepetition frequency of 5000 per second and higher. In place ofcontrolling the total flash duration by start-ing and stopping the cam33, the same effect may be obtained by controlling the peaked voltagewave generator by operation of the switch 36, or in any other suitablemanner.

In other words, since, in the example of Fig. 3, the maximum flashingrate of the tube 1 3 of 60 flashes per second is a substantialsubmultiple of the repetition frequency of the ionizing or switchingpulses p, the tube 13 is directly intermittently connected to the source22 during the conducting periods At, Fig. 2, of the switching tube 28,whereby to result in an incremental direct energy supply to the flashtube 13 from the source 22, in addition to the energy stored by thecapacitor 30. At the same time, the intermittent operation of theswitching tube 28, acting as a protective impedance for the flash tube13, prevents a dangerous build-up of the direct source current to avalue liable to damage the tube or other circuit elements.

Referring to Fig. 6, there is shown a modified system according to theinvention for producing a series of discharges of equal intensity andlength during each alternation a of the operating current. The circuitshown difiers from the circuit of Fig. 3 by the provision of a singletransformer 25 supplying operating voltage to both the ionizing pulsegenerator 27 and to the flash tube 13. Furthermore, both the tube 28 andflash tube 13 are shown to be controlled directly by the ionizingpulses, that is, without the aid of any special starting electrodes. Forthis purpose, the tube 13 may be of a relatively short length to cause adischarge at about one-third of the full operating voltage. In a systemof this type, upon closing of the switch 36, the supply voltage andionizing pulses are continuously and simultaneously applied to both theswitch tube 28 and flash discharge tube 13 in series, in such a mannerthat, provided a proper design of the circuit constants and parameters,equally high intensity discharge flashes will be produced during eachpositive alternation a, as shown and further understood by reference toFigs. 7 and 8 of the drawing. At the same time,

the size of the capacitor 30 is further reduced. For practical purposes,the capacitor may be designed to supply only about 2% of the total powerdissipated in the flash, the remaining 98% being supplied by the powersource 22 through transformer 25. As a result, a capacitor with acapacitance as low as 8 mfd. has been found suitable for the purpose ofthe invention.

The operation of the circuit according to Fig. 6 is as follows. The peakvoltage generator 27, having its anode energized by the alternatingvoltage supplied by the transformer 25, begins to function only with aniinimum voltage 2 during the positive alternations a, as shown at PFig. 7, atwhich point the tube 28 is ionized by the applied high voltagepulse 'p,'thereby'. charging the capacitor 30. Assuming an operatingvoltage of 1500 volts supplied by the transformer and a critical orbreakdown voltage 2 of the flash tube 13 of about onethird this value,that is, 500 volts, the tube 13 will be ionized upon reaching point P ofthe alternation, thus initiating a high intensity ionicdischarge f, Fig.8, which is instantly reinforced by a substantial current or energycomponent 1 directly from the source 22 through the transformer 26, thetube 28 offering a relatively low impedance during the duration of thepulses p. At the same time, the duration of the flash is extended toabout one-third of the alternation, that is ,4 see. in the case of a60-cycle power supply.

The flash is extinguished when the tube 27 ceases to supply ionizingpulses p at the point P of the alternation, thus increasing theimpedance of the tube 28 until the next operating cycle or alternationa. As a result, substantially all the power dissipated in the flash andconverted into light energy is supplied by the source 22, the capacitor30 merely serving to determine the initiation of the flashes during eachalternation and to thereby stabilize the action repeated during eachsuccessive alternation. This, in turn, results in a practicallycontinuous light output which may be controlled both in intensity and/orduration to suit any existing conditions and requirements.

In the simplified circuit as shown, the ionizing pulses 2, shown in theform of straight lines in Fig. l, are directly superimposed upon theoperating voltage pulses or alternations a, it being understood that thedischarge control may be effected by means of an additional startingelectrode, in the manner shown in Fig. 9. The latter further differsfrom Fig. 6 by the provision of a separate power supply for the flashtube and ionizing pulse generator in the form of two transformers 25'and26, re-

spectively. The invention also provides a simple means for and method ofcontrolling the total flash output and or duration of the individualflashes by varying the amount of the supplementary energy in anysuitable manner, such as by controlling the voltage of the power sourceby means of a step transformer, as shown at 35 in Fig. 9, or by anyother suitable means.

Fig. 10 shows a simple D.C.-operated flash lighting system according tothe invention comprising a battery 40 or the like, the switching tube 28and ionizing pulse generator 41, all connected in series with thestabilizing capacitor 30 which is shunted across the flash tube 13. Inoperation, tube 28 is first ionized by a pulse p, Fig. 12, to charge thecapacitor 30. After the latter has been charged to a sufficient voltage,the flash tube 13 becomes in turn ionized, producing an instantaneouslight flash j by the capacitor discharge followed by a supplementarycomponent f directly supplied by the source 40. All this happens withinthe duration of a single pulse p, thus resulting in a continuous seriesof highintensity light flashes at the ionizing pulse recurrencefrequency.

Fig. 11 shows a modification of a D.C.-flash' lighting system includingmeans to produce a series of trains of light flashes of greater durationfor use as a beacon light or the like. For this purpose there is shuntedacross the capacitor 30 a self-running relaxation oscillator producing aperiodic ionizing potential at a sub-multiple of the recurrencefrequency of the pulses p, and being applied to the starting electrode16 of the flash tube 13. The ionizing oscillator shown comprises aresistor 43 in series with a'capacitor 44, the latter'bein'g shunted bya simultaneously by the source 40 discharges through the tube 13 duringthe time t as shown at c, causing thereby an instantaneous light flash ffollowed by a supplementary discharge 1 directly from the source 40. Bythe proper choice of the frequency of the relaxation oscillatordetermined by the resistor 43 and capacitor 44, intermittenthigh-intensity light flashes may be produced of any desired length andspacing intervals.

Again, since the frequency of the ionizing oscillators 43, 44, 45determining the flashing rate of the tube 13 is a substantialsubmultiple of the peaked pulse wave generator 41, the tube 13 will beintermittentily directly connected to the source 40 through theswitching tube 28 during a flash discharge period, to result in anincremental direct energy supply to the tube 13.

In Fig. 11, the ionizing pulse voltage generator 41 is shown in the formof a transistor blocking oscillator to reduce weight and bulk of theapparatus when used as an emergency beacon or the like. 'In order tofurther improve the operation and to reduce the drain on the battery 40,the latter is advantageously shunted by a further stabilizing capacitor48 of suitable size.

If the device is used as an emergency light beacon, it may be simplycombined with a distress radio signal transmitter by causing the voltagepulses p to shock excite a resonant transmitting circuit 50 connected toan antenna 51, to produce a series of damped radio wave trains asindicated at r in Fig. 13. of an accident can be ascertained first bythe bearing of the long-range radio signal and thereafter by aclose-range light beacon.

In the foregoing the invention has been described'with reference to afew specific and illustrative devices; It will be evident, however, thatchanges and variations, as well as the substitution of equivalent partsand circuits for those shown, may be made without departing from thebroader spirit and scope of the invention as set forth in the appendedclaims. are accordingly to be regarded in an illustrative rather than ina limiting sense.

This application is a continuation-in-part of my application Serial No.495,636, filed on March 21, 1955 encharge thereof through said tube in aseries of luminous flash discharges having a predetermined repetitionfre quency, and further means producing a series of peaked high-voltagepulses having a repetition frequency equal to a substantial multiple ofsaid first repetition frequency and controlling said device, to causealternate conducting and non-conducting periods thereof resulting in anintermittent incremental energy supply directly from said source to saidtube during a flash discharge period.

2. A capacitor flash light system comprising a gaseous flash dischargetube, a capacitor connected in parallel to said tube, a gaseousswitching tube, a source of energy connected to saidcapacitor in serieswith said switching In this manner, the location The specification anddrawings 9 tube, means to effect an alternate charging of said capacitorby said source through said switching tube and a discharge thereofthrough said flash tube in a series of luminous flash discharges havinga predetermined repetition frequency, and funther means producing aseries of peaked high-voltage pulses having a repetition frequency equalto a substantial multiple of said first repetition fre quency, toperiodically ionize said switching tube and to cause alternateconducting and non-conducting periods thereof resulting in anintermittent incremental energy supply directly from said source to saidflash tube during a flash discharge period.

3. In a capacitor flashing light source as claimed in claim 2, said lastmeans being connected in series with said source and said switchingtube.

4. In a capacitor flashing light source as claimed in claim 2, anionizing electrode for said switching tube, said last means beingconnected to said electrode.

5. In a capacitor flash light system as claimed in claim 2, said firstmeans consisting in said source being an alternating current sourcedesigned to effect a charge 10 of said capacitor during a predetermined,including unity, number of positive half-cycles of said source, and saidlast means producing a series of peaked high-voltage pulse trains duringand in synchronism with said positive halfcycles of said source.

6. In a capacitor flashing light source as claimed in claim 2, saidsource being a direct current source and said first means including arelaxation oscillator having a frequency equal to a submultiple of saidlast-mentioned frequency, and means to periodically ionize said flashtube by said oscillator.

References Cited in the file of this patent UNITED STATES PATENTS1,979,692 Knowles Nov. 6, 1934 2,310,092 Knowles Feb. 2, 1943 2,331,317Germeshausen Oct. 12, 1943 2,478,905 Edgerton Aug. 16, 1949 2,491,342Townshend Dec. 13, 1949 2,492,247 Weaving Dec. 27, 1949

